i have tried using the area of region (0, 0) (0,1) (1,0) and multiplying this with the equation under the closed integral
ie is integrate(f.da) gauss theorem
Using the Green's theorem, $\displaystyle \int_C(x-y)dx+(x+y)dy=\iint_D(1+1)\;dxdy=2A$ where $\displaystyle A$ is the area of the triangle.